CN101835072B - Virtual Surround Sound Processing Method - Google Patents

Abstract

The virtual surround sound processing method of the present invention comprises the following steps: measuring the transfer function HRTF (c, 0) at the virtual sound source point N; determining the horizontal distance between the unknown virtual sound source point M and the center of the human brain as f; Through the two ears of the human brain and the point M of the virtual sound source point to be known, two straight lines are respectively drawn to intersect the circle where the virtual sound source point N is located to point L and point P, and the points L and P are respectively connected to y The angle formed by the axes is a, b, and the transfer function HRTF of the angle a and the angle b are respectively HaR, HaL, HbR, HbL; according to the measured transfer function HRTF of the virtual sound source point N, deduce HaR, HaL, HbR, HbL; input R*HaR to the right ear, and input R*HbL to the left ear to obtain the virtual sound source point M to be known. The virtual surround sound processing method of the present invention has the characteristic of reducing the times of measuring transfer function HRTF to obtain the virtual sound source point to be known.

Description

Virtual Surround Sound Processing Method

technical field

The invention relates to a virtual surround sound processing method for an earphone sound system.

Background technique

When listening to stereo music with headphones, in order to increase the sense of envelopment of the stereo, we will use the method of virtual surround sound to process the music signal to generate virtual sound sources with different angles and directions, and add them to the original music signal to increase the sound quality of the music. A sense of envelopment and three-dimensionality.

Due to the auricle effect of the human ear, the spectral characteristics of the sound wave reaching the eardrum are related to the direction of the sound source. The human auditory system is functionally equivalent to a filter related to the spatial direction of the sound, and the spectral information of the sound in different spatial directions , are all processed by this filter to reach the eardrum, and this frequency characteristic is called the Human Brain Audio Transformation Function HRTF (Head-Related Transfer Function).

When virtualizing sound sources from different directions, the transfer function HRTF is needed. For example, the input music signal is divided into L signal and R signal, and when the virtual sound source is in the virtual horizontal direction and at an angle of 60 degrees to the earlobe line of the human brain, the transfer function HRTF in this direction needs to be used, that is, HRTF(60,0 ).

Figure 1 is a schematic diagram of the transmission path of the HRTF function in which the sound source point A is at an angle of 60 degrees to the earlobe line of the human brain. In Figure 1, the 60-degree direction refers to the angle between the center of the human brain and the y-axis. When the sound source point A is located in the 60-degree direction, the transfer function HRTF to the left ear is H60L, and the transfer function HRTF to the right ear for H60R. Due to axial symmetry, the transfer function HRTF for a sound source located in a 300-degree direction is H60R to the left ear and H60L to the right ear.

The transfer function HRTF needs to be measured by the human brain and audio test system. Assuming that the data of the transfer function HRTF at a distance of 1.4m from the sound source has been measured, a virtual sound source at a distance of 1.4m from the center of the human brain can be virtualized:

To virtualize the L signal into a sound source in a 300-degree direction, you need to input L*H60R into the left ear, and L*H60L into the right ear;

To virtualize the R signal into a sound source in a 60-degree direction, R*H60L needs to be input to the left ear, and R*H60R is input to the right ear; where * represents convolution.

At this time, the virtual sound source point A at a distance of 1.4m from the center of the human brain and an azimuth of 60 degrees can be obtained from the transfer function HRTF.

If it is necessary to obtain the data of the virtual sound source point at other distances from the center of the human brain, such as the data of the virtual sound source point at a distance of 0.3m from the center of the human brain, it is necessary to measure the transfer function HRTF at 0.3m again. However, measuring the transfer function HRTF each time is not only complicated but also time-consuming.

From this point of view, it is necessary to provide a virtual surround sound processing method, which can effectively reduce the number of HRTF measurement transfer functions to obtain virtual sound source points.

Contents of the invention

Aiming at the complicated and time-consuming problem of measuring transfer function HRTF in the prior art, the present invention provides a virtual surround sound processing method that effectively reduces the number of transfer function HRTF measurements to obtain a virtual sound source point.

A virtual surround sound processing method, comprising the following steps:

Provide an earphone with a built-in processing chip, the head-related transfer function HRTF is pre-stored in the processing chip, and the transmission HRTF function (c, 0) of the virtual sound source point N is measured, taking the center of the human brain as the origin, and the human brain's two ears The vertical line of the connecting line is the y-axis to build a coordinate system, and the angle between the connecting line from the virtual sound source point N to the origin and the y-axis is that the azimuth angle of the virtual sound source point N is c;

Determine the horizontal distance between the virtual sound source point M to be known and the center of the human brain as f and the virtual sound source point M to be known is at the same azimuth as the virtual sound source point N;

With the origin as the center of the circle, the distance between the virtual sound source point N and the origin is used as a radius to make a circle, pass through the ears of the human brain and the virtual sound source point M to be known, and draw two straight lines to the location where the virtual sound source point N is located. The circle intersects to point L and point P, the angles formed by the point L and point P and the y-axis are a and b respectively, and the transfer function HRTF of the angle a and angle b are respectively HaR, HaL, HbR, HbL ;

The processing chip derives HaR, HaL, HbR, HbL according to the measured transfer function HRTF of the virtual sound source point N;

The earphone inputs R*HaR to the right ear and R*HbL to the left ear to obtain the virtual sound source point M to be known.

As a further improvement of the above virtual surround sound processing method, when the music signal input to the headphone audio system is divided into L signal and R signal, the music signal after virtual surround processing should be:

Lout=mxL+L*HaR+R*HbL;

Rout=mxR+R*HaR+L*HbL, where * represents convolution, and m is a coefficient, which refers to adjusting the ratio of the original signal to the processed signal.

As a further improvement of the above virtual surround sound processing method, the virtual sound source point N is obtained by inputting R*HcL to the left ear and inputting R*HcR to the right ear.

As a further improvement of the above virtual surround sound processing method, the azimuth c of the virtual sound source point N is 60 degrees.

As a further improvement of the above virtual surround sound processing method, the distance between the virtual sound source point N and the center of the human brain is 1.4m.

As a further improvement of the above virtual surround sound processing method, the horizontal distance f between the unknown virtual sound source point M and the center of the human brain is 0.3m.

In the virtual surround sound processing method of the present invention, it is only necessary to measure the transfer function HRTF of a certain virtual sound source point, and on the basis of the measured transfer function HRTF value, it can be deduced by the method of geometric drawing in the same direction, Another virtual sound source point in a different horizontal direction, reducing the number of times to measure the transmitted HRTF.

In summary, the virtual surround sound processing method has the characteristic of reducing the number of HRTF measurement transfer functions to obtain virtual sound source points.

Description of drawings

Fig. 1 is a schematic diagram of the HRTF function transmission path related to the present invention.

Fig. 2 is a schematic diagram of the HRTF function transmission path in the virtual surround sound processing method of the present invention.

Fig. 3 is a time-domain diagram of the impulse response of the HRTF function (60, 0) in Fig. 2 .

Detailed ways

The virtual surround sound processing method of the present invention will be described below with reference to the accompanying drawings.

The present invention provides a virtual surround sound processing method, the main purpose of which is how to obtain virtual sound source points at the same azimuth but in different horizontal directions through the measured transfer function HRTF of a virtual sound source point in a certain azimuth.

Fig. 2 is a schematic diagram of the HRTF function transmission path of the virtual surround sound processing method of the present invention. In Fig. 2, the center of the human brain is taken as the origin, and the vertical line connecting the two ears of the human brain is the y-axis to establish a coordinate system, and the angle between the line from the virtual sound source point N to the origin and the y-axis is the virtual sound source point N. The azimuth angle of the source point N is c; the virtual sound source point N is along the horizontal direction and forms an azimuth angle of c degrees with the earlobe line of the human brain, and the transfer function HRTF in this direction is HRTF(c, 0). In this embodiment, c is 60 degrees.

Fig. 3 is the impulse response time domain diagram of HRTF (60, 0). In Figure 3, the upper figure shows the transfer function H60L of the left ear, and the lower figure shows the transfer function H60R of the right ear. The transfer function HRTF needs to be measured by using the human brain and an audio test system. The transfer function HRTF in FIG. 3 is the data measured at a distance of 1.4m from the virtual sound source point N in the horizontal direction of the human brain.

The 60-degree azimuth of the virtual sound source point N refers to the angle between the center of the human brain as the origin and the y-axis, and the transmission to the left ear of the human brain is set when the virtual sound source point N is located at an angle of 60 degrees. The function HRTF is H60L, and the transfer function HRTF to the right ear of the human brain is H60R.

When the music signal input to the earphone audio system is divided into L signal and R signal, the virtual sound source point N along the horizontal direction and 1.4m away from the center of the human brain can be virtualized by using the data in Fig. 3:

To virtualize the L signal into a sound source in a 300-degree direction, you need to input L*H60R into the left ear, and L*H60L into the right ear;

To virtualize the R signal into a sound source in a 60-degree direction, you need to input R*H60L into the left ear and R*H60R into the right ear;

Then, the music signal after virtual surround processing should be:

Lout=mxL+L*H60R+R*H60L;

Rout＝mxR+R*H60R+L*H60L

Among them, * represents convolution, and m is a coefficient, which refers to adjusting the ratio of the original signal to the processed signal.

In this way, the virtual sound source point N in FIG. 2 represents a virtual sound source point 1.4m away from the center of the human brain and with an azimuth of 60 degrees. That is to say, if you put R*H60L into the left ear and R*H60R into the right ear, you can feel the sound coming from that point.

Then, the horizontal distance from the center of the human brain to the center of the virtual human brain is f using the data of the measured transmission function HRTF at 1.4m, and the virtual sound source point M to be known is at the same azimuth as the virtual sound source point N, which is the same as that of the human brain. The vertical line of the binaural connection is the second position where the angular direction is still 60 degrees, that is, the virtual sound source point M to be known. In this embodiment, f takes 0.3m.

The specific method is as follows:

As shown in Figure 3, take the origin as the center of the circle, the distance between the virtual sound source point N and the origin is the radius to make a circle, and draw two straight lines through the ears and the virtual sound source point M to be known and take the center of the human brain as a circle point , 1.4m is a circle with a radius intersecting to point L and point P to obtain a dotted line OL and a dotted line OP. The angle formed by the dotted line OL and the y-axis is set as a, and the angle formed by the dotted line OP and the y-axis is set as b. Since the first sampling points of the HRTF function are approximately zero, it corresponds to the transmission delay from the sound source to both ears, that is, the sampling value in the time it takes for the sound to transmit from the sound source to both ears is zero. In Figure 3, the transfer functions from point L to the right ear and from point M to the right ear are different in the first few zero value sampling points. Value sampling points are different. The difference between the sampling points from point L to point M and from point P to point M is only a few points at most, which can be approximated as equal. Therefore, the transfer function HRTF of angles a and b can be used instead of the transfer function HRTF of 60 degrees.

That is to say, as long as the transmission functions HRTF, HaR, HaL, HbR and HbL of angle a and angle b at 1.4m are known, the virtual sound source point M to be known can be virtualized: input R*HaR to the right ear , input R*HbL to the left ear, and you can feel that the sound is emitted from the to-be-known virtual sound source point M.

According to the principle of axial symmetry, the virtual sound source of the virtual sound source point M to be known can also be virtualized at another point on a circle with a radius of 0.3m symmetrical to the y-axis: input L*HbL to the right ear, and L *HaR can be input to the left ear. The music signal after virtual surround processing should be:

Lout=mxL+L*HaR+R*HbL;

Rout=mxR+R*HaR+L*HbL,

The virtual surround sound processing method of the present invention, through the measured transfer function HRTF data at 1.4m, utilizes the geometric drawing method to obtain angle a and angle b, and then according to the measured transfer function HRTF (60, 0) value, the transfer function HRTF value at 0.3m can be deduced, without the need to measure the transfer function HRTF value at 0.3m again, and the number of times to measure the transfer function HRTF can be reduced to obtain the desired virtual sound source point M to be known .

Therefore, the virtual surround sound processing method of the present invention only needs to measure the transfer function HRTF of a certain virtual sound source point, and can derive the same orientation, Another virtual sound source point in a different horizontal direction, reducing the number of times to measure the transmitted HRTF.

The calculation of the HRTF function can be processed by means of a processing chip built in the earphone, and the HRTF function is pre-stored in the processing chip.

To sum up, the virtual surround sound processing method has the characteristics of reducing the number of times of measuring and transmitting HRTF functions to obtain virtual sound source points.

The above are only preferred implementation examples of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (6)

1. A virtual surround sound processing method for an earphone sound system, comprising the following steps: Provide an earphone with a built-in processing chip. The head-related transfer function HRTF is pre-stored in the processing chip, and the transfer function HRTF(c, 0) of the virtual sound source point N is measured. Taking the center of the human brain as the origin, the human brain double The vertical line of the ear connection is the y-axis to build a coordinate system, and the angle between the line from the virtual sound source point N to the origin and the y-axis is the azimuth angle of the virtual sound source point N as c; Determine the horizontal distance between the virtual sound source point M to be known and the center of the human brain as f and the virtual sound source point M to be known is at the same azimuth as the virtual sound source point N; With the origin as the center of the circle, the distance between the virtual sound source point N and the origin is used as a radius to make a circle, pass through the ears of the human brain and the virtual sound source point M to be known, and draw two straight lines to the location where the virtual sound source point N is located. The circle intersects to point L and point P, the angles formed by the point L and point P and the y-axis are a and b respectively, and the transfer function HRTF of the angle a and angle b are respectively HaR, HaL, HbR, HbL ; The processing chip derives HaR, HaL, HbR, HbL according to the measured transfer function HRTF of the virtual sound source point N; The earphone inputs R*HaR to the right ear and R*HbL to the left ear to obtain the virtual sound source point M to be known. 2. virtual surround sound processing method according to claim 1, is characterized in that: when the music signal of input earphone sound system is divided into L signal and R signal, by the music signal after virtual surround processing should be: Lout=mxL+L*HaR+R*HbL; Rout=mxR+R*HaR+L*HbL, where * represents convolution, and m is a coefficient, which refers to adjusting the ratio of the original signal to the processed signal. 3. The virtual surround sound processing method according to claim 2, wherein the virtual sound source point N is obtained by inputting R*HcL to the left ear and inputting R*HcR to the right ear. 4. The virtual surround sound processing method according to claim 3, characterized in that: the azimuth c of the virtual sound source point N is 60 degrees. 5. The virtual surround sound processing method according to claim 4, characterized in that: the distance between the virtual sound source point N and the center of the human brain is 1.4m. 6. The virtual surround sound processing method according to claim 5, characterized in that: the horizontal distance f between the unknown virtual sound source point M and the center of the human brain is 0.3m.

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